Effect of thymoquinone on odontogensis of human dental pulp cells
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BACKGROUND: Thymoquinone (TQ) is one of the most active ingredients of Nigella sativa seed. TQ has a variety of pharmacologic properties including possess antinociceptive, antibacterial, anti-inflammatory, anti-oxidative activities and osteogenic effects on bone cells. Because of these properties, TQ might play an important role in odontogenic effects on human dental pulp cells and be used as a pulp capping material. PURPOSE: This study evaluates the effect of TQ on the attachment efficiency, proliferation, and odontogenic differentiation of Human Dental Pulp Cells (HDPC's). The effect of TQ on odontogenic differentiation was also determined by evaluating alkaline phosphatase (ALP) activity and Dentin Sialoprotein (DSP) expression. METHODS: Human dental pulp cells were cultured in triplicate using growth media with various TQ concentrations: 5 μM, 10μM, 15μM, 30μM, and 0μM as a control group at 7 and 21 days. Crystal violet staining was used to determine cell attachment efficiency and cell proliferation. The proliferation rates were normalized to cell numbers of each group at 16 hours. Cell differentiation was assessed by evaluating ALP activity and DSP expression. The data were normalized on per million cells basis. Univariate analyses including ANOVA and Student’s t-test were conducted. RESULTS: Higher cell attachment efficiency was shown in all TQ groups at 16 hours (P<. 0001) except for the 5 μM group. A significantly higher cell proliferation rate was shown with low TQ concentration 5 μM at 7 days (P<. 0001) and at 21days (P<. 0.05). However, the cell proliferation rates decreased significantly with higher TQ concentrations at both time intervals (P< 0.0001). Similarly, prolifration rates decreased at 21 days TQ =10 μM (P< 0.0001) and TQ =15 μM (P=0.0006). Significantly higher levels of alkaline phosphatase activity were observed in all TQ groups at 7 days (P <0.0001) and at 21 days (P <0.0001). Dentin sialoprotein expression was significantly down regulated in all TQ groups at 7 days compared to the control (P <0.05), however, at day 21 only TQ =15 μM exhibited significant down regulation of DSP compared to the control (P <0.0001). CONCLUSION: All tested TQ concentrations significantly enhanced cell attachment efficiency at 16 hours except TQ =5 μM. Cell proliferation rates were increased significantly by low TQ concentration 5 μM, and decreased significantly with higher TQ concentration 30 μM at 7 and 21 days. TQ exhibits odontogenic potential by inducing a significant increase in ALP activity at 7 and 21 days. TQ did not have any effect on DSP expression at 21 days except TQ =15 μM which significantly decreased DSP expression.